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Soil Permeation Grouting

Soil Permeation Grouting is typically used to reduce soil permeability, improve soil cohesion, improve the structural characteristics of the soil, or, as often the case, a combination of some or all of these goals. It involves the injection of grout at low pressures into the soil matrix in an effort to permeate or encapsulate the individual soil grains without otherwise disturbing the natural state of the soil.

Sleeve pipes are the key enabling apparatus involved. They are installed prior to grouting by being placed and encapsulated in a weak mix of bentonite and cement in a series of drilled holes intersecting the target soil mass. A sleeve pipe, typically 38 mm to 75 mm diameter PVC or steel pipe, contains several sets of small holes along its length that are enveloped by protective, expandable, rubber sleeves. The sleeves act as one-way valves, keeping fluids outside the pipe from getting in, but allowing fluid on the inside - once sufficiently pressurized - to get out. A device called a packer is used to isolate one or more sleeves at a time. Grout is injected via the grout pump at surface, through the grout tube to the packer, then finally across the sleeve and into the interstitial space between the individual soil grains.

Grout is injected into the soil slowly and under relatively low pressure in order to avoid excessive hydrofracturing of the soil. Grout spread is governed by soil type, degree of soil compaction, grain size distribution, grout type (eg. solution or suspension), gel time, grout rheology and grouting pressure. Real time monitoring of pressure, flow and cumulative grout take is used to constantly evaluate and determine the direction of the grouting program. Its implementation also conveniently results in measurement of the completed work for compilation of records and computation of useful data such as theoretical grout spread and determination of the hydrofracturing threshold.

Geo-Foundations has completed a number of soil permeation grouting projects involving cement grouts, microfine cement grouts, sodium silicate grouts, acrylate grouts and polyurethane grouts. This technology is particularly useful in sandy soils with less than 20% fines. A common application is pre-treatment of cohesionless soils close to sensitive structures to prevent undermining the structure during excavation or tunnelling.

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